Marijuana Use Takes Toll on Adolescent Brain Function

Sean Johnson

The brains of teens who use marijuana are working harder than the brains of their peers who abstain from the drug.

Krista Lisdahl Medina, a University of Cincinnati assistant professor of psychology, with the help of Susan Tapert, associate professor of psychiatry at the University of California, San Diego recently found that the brains of teens who use marijuana “are working harder than the brains of their peers who abstain from the drug.” Medina’s presentation on the topic, entitled “Neuroimaging Marijuana Use and its Effects on Cognitive Function,” was held at the 2008 meeting of the American Academy of Pediatrics earlier this month. Medina said that her research suggests that “chronic, heavy marijuana use during adolescence—a critical period of ongoing brain development—is associated with poorer performance on thinking tasks, including slower psychomotor speed and poorer complex attention, verbal memory and planning ability.” She also noted that, although studies have shown that partial recovery of verbal memory functioning within the first three weeks of abstinence from the drug is possible, “complex attention skills continue to be affected.”

The recent research also suggested that girls are more prone to these neurocognitive consequences. Studies found that teenage girls who did smoke marijuana had larger prefrontal cortex (PFC) volumes than those who did not, and the larger PFC volumes were associated with “poorer executive functions of the brain in these teens, such as planning, decision-making or staying focused on a task.”

This research stresses what researchers have known for some time; adolescence is a critical time of brain development. More studies need to be conducted to determine the extent of the damage that marijuana has on the adolescent brain. “Longitudinal studies following youth over time are needed to rule out the influence of pre-existing differences before teens begin using marijuana, and to examine whether abstinence from marijuana results in recovery of cognitive and brain functioning,” said Medina.